The overall goal of these studies is to define the role of Schwann cell gap junctions in the development and regeneration of peripheral nerve. The primary hypothesis is that mature myelinating Schwann cells express the gap junction protein Cx32 in the form of reflexive contacts between paranodal and Schmidt-Lantermann incisures of single cell, whereas proliferating Schwann cells in early development and distal to the site of nerve injury express another gap junction protein (identified as Cx46) that provides intercellular coupling functioning to coordinate maturation and response to injury. Because point mutations in Cx32 are responsible for the X-Linked form of Charcot-Marie Tooth syndrome (CMTX), a demyelinating peripheral neuropathy, we will correlate changes in Cx32 expression with myelination in vivo and in culture in normal animals and we will compare these findings with studies of Schwann cell maturation and remyelination in Cx32 and Cx46 knockout animals. Because expression of Cx46 and the proliferating phenotype are induced in Schwann cells by nerve injury, we will examine the time course of changes after nerve injury and during regeneration. The proposed studies will define both in vitro and in vivo: 1) The connexins expressed by Schwann cells at specific stages of maturation; 2) The changes in connexin expression that occur in peripheral nerve following injury and during remyelination; 3) The effects of mitogens released during and following nerve injury on gap junction expression and function in cultured Schwann cells; and 4) The effects of altered connexin expression on proliferative and differentiation responses of Schwann cells in culture and in nerve. Together, the broadly based studies proposed in this application should greatly extend our knowledge of the cell biology of the Schwann cell and its modulation in pathological conditions.